In recent years emphasis has been placed upon the development of systems for holding automobile passengers in their seats during the sudden deceleration experienced as a result of a collision. Seat belts and shoulder harnesses have been shown to be effective to decrease both the frequency and the severity of injuries resulting from automobile accidents. However, these devices suffer from one major drawback. They must be buckled by the passenger. The widespread failure on the part of the motoring public to "buckle up" has led to a demand for devices which will hold the passenger in his seat without the need for any overt act. Such a passive restraint system would be built into the automobile and be automatically activated upon a collision.
One promising passive restraint system is the inflatable gas cushion or crash bag. In this system, a flow of gas is employed to rapidly fill a flexible bag upon activation of the system. The inflated bag provides cushioning during the rapid deceleration, thus preventing contact of the occupant with the car interior and reducing the chance of serious injury during an accident. After the initial contact, the bag slowly deflates to avoid entrapment of the passenger. During this process, gases employed to inflate the bag also escape into the atmosphere surrounding an occupant. Thus, the gases must not in themselves be detrimental to human health since the benefits of the restraint system would then be lost.
One type of crash bag system employs high pressure nitrogen stored in a gas bottle to fill a bag. Activation of the unit releases the nitrogen which flows into the bag. Such a stored gas system is undesirable from the standpoint of cost and poor adaptability to automotive styling caused by its size and weight. An alternative to the compressed gas system lies in the use of a pyrotechnic gas generator. In this system, a small pyrotechnic charge is set off upon activation and upon burning evolves sufficient gas to fill the bag. This type of system offers a cost advantage as well as adaptability to a relatively compact light weight generating device such as that disclosed in a copending application entitled "Gas Generator," filed in the U.S. Pat. Office by Gerald R. Staudacher, et al. on July 31, 1972 as application Ser. No. 276,397.
In order for a pyrotechnic to be useful in such a system, the composition of the pyrotechnic must meet several criteria. First, the composition must release sufficient gas to fill a bag of suitable volume to a pressure of at least about one psig. within 20 to 60 milliseconds after ignition. Secondly, the gases released upon ignition of the pyrotechnic composition should not be toxic to the automobile occupants. In addition, the gas produced should not increase the temperature of the bag to the point of causing serious thermal injury or pain. Furthermore, the noise level upon functioning should remain below about 170 DB and preferably below 150 DB. A further requirement is that such a composition should remain operable between temperatures ranging from about -20.degree. to about 220.degree.F.
It is an object of the present invention to provide a method and composition for inflating crash bag type passive restraint systems which meets or exceeds the above criteria.